Floating dry dock



July 28, 1 942. F. R. HARRIS FLOATING DRYDOCK Filed May l] l rialWITNESSiES INVE OR Patented July 28, 1942 I Urrso srrss sereni OFFICEFLOATING DRY DOCK Frederic R. Harris, New York, N. Y.

Appiication May 11, 1940, Serial No. 334,646

4 Claims.

My invention relates to an improvement in floating dry docks, and it isespecially adapted for use in dry dock pontoons that are constructed oftimber.

The object of my invention is to provide a strong, compact and economictransverse pontoon truss adapted to support a heavy ship load, which isshored on the center line of the dock.

Hitherto dry dock pontoons are given a rectilinear and rectangular boxshape, to which form the pontoon trusses conform.

Therefore, in a conventional dry dock pontoon, a centrally located shipload is supported by a water pressure of constant intensity everywhereunder the fiat pontoon bottom, and the transverse trusses therein mustobviously be designed to carry not only the direct tension in the bottomchords due to the central ship load, but also the tension due to thebending of the rectilinear chord segments between panel points.

Now, however, I have discovered that by means of providing a roundbottom in the pontoon and truss chords conforming with the pontoonbottom, the bottom chord tension, instead of being augmented by theoutside water pressure, will be substantially reduced by a countereffective arch compression in the sprung chord segments between adjacentpanel points.

Besides a substantial stress reduction in the main truss member, othermajor advantages that ow from my invention are as follows:

The cross section of my preferred dry dock pontoon is massed towards thecenter thereof, and the direct stresses due to the ship load arematerially reduced.

The free water surfaces inside my preferred pontoon structure willgradually contract as pumping proceeds, and a considerable reduction ofdock width, i. e., truss span, is possible as relatively narrow wingwalls will suffice to stabilize the dock and the ship shored thereonduring the docking operation.

In the drawing: Fig. 1 is a cross section of the dry dock and shows mypreferred construction of a transverse pontoon timber truss. Fig. 2 is afractional longitudinal cross section of the dry dock itself and shows aseries of transverse trusses supporting the outside planking thereof.

Referring to the drawing, in which like reference characters designatecorresponding parts, I denotes a iloating dry dock comprising a pontoonstructure 2 which at its ends supports upright side walls or wings 3.

In the pontoon body 2 a transverse truss 4 is shown'provided with apreferably laminated bottom arch chord 5, in the upper side of whichdiagonally placed struts 6 are notched.

I prefer to fan out said struts from a point at the center of the trussdirectly under the ship load 1, and in my preferred truss construction asecond laminated and arched truss member 8 is sprung over the top of thestruts 6 and the bend down ends of the arched member 8 are connected tothe outer end portions of the bottom chords by means of suitable chocks9 and wedges ID, all held together as a rigid corner by suitable throughbolts II.

I prefer also in my pontoon construction to lay the deck planking I2directly on top of the top truss chord members I3, but I prefer tosupport the bottom planking I4 on floor beams I5 laid across the bottomchords 5.

Suliicient truss uprights I6 are also provided in the pontoon truss andtted between the top and bottom chords and the laminated members, theirfunction being to transmit the external water pressures from deck tobottom when the dock is submerged, and also render the pontoon trussrigid when the dock is up.

Sufficient ballast, not shown in the drawing, is placed inside the dockstructure so as to sink the dock when ilooded.

It is evident that when the dry dock pontoon supports a maximum ship,the pontoon deck will be approximately awash, and it is also evidentthat the pontoon truss should be designed to carry the maximum shipload.

When a ship is being docked and is just clearing the water, the entiredock stability is due to the side walls, which must balance the elevatedship moment as well as the upsetting moments due to the inside freewater surfaces in the pontoon.

Obviously, in my preferred construction the free water moments grow lessthe more the pontoon is pumped out, while said moments remain constantin the conventional rectangular pontoon.

The inner free water is thus reduced to a minimum for a maximum shipload, and the width of the dry dock can therefore be materially reduced.

I do not wish to limit my claims to the construction shown as it isevident that alterations and modications may be made in the adaptationof my device for different purposes without departing from the spiritand scope of my invention.

I claim:

l. A oating dry dock pontoon comprising a round bottom, a deck, and atransverse truss between the bottom and deck, said truss including anarched bottom chord member curved to the shape of the round bottom andto which the bottom is connected, and diagonal braces extending from acentral line of the pontoon deck to spaced panel points along theconcave side of the arched bottom chord member, said panel points beingso spaced from one another along the arched member that the waterpressure exerted against the pontoon bottom and transmitted from saidbottom to the portions of the arched bottom chord member between panelpoints compresses the arched portions with a Y' force that substantiallyrelieves the tensioning of said bottom chord member by the load of aship centrally located on the deck above the diagonal braces.

`down ends of said arched truss member to the end portions of the bottomchord member.

- 4. In a oating dry dock pontoon, having a round bottom section, atimber truss for sus- 2. A oating dry dock pontoon comprising a roundbottom, a deck, and a timber truss between the bottom and the deck forsustaining a central ship load, said truss including a laminated andarched bottom chord member conforming with the outline of the pontoonbottom and to which the Water pressure against the bottom istransmitted, struts fanning out from a point close to and below thepoint of load application and notched in the top side of the archedbottom chord member at spaced points along said member, and means thattransmit bottom pressure to the arched segments of the chord memberbetween said spaced points so as to cause a substantial arch compressionin the bottom chord member that substantially relieves the tensionstress therein.

i taining a central ship load, comprising a laminated and arched bottomchord member conforming to the shape of the pontoon bottom, strutsfanning out from a point close to and below the upper central region ofthe truss and extending to spaced panel points along the concave side ofthe arched bottom chord member, means for transmitting the bottompressure to the arched chord member so as to cause a substantial archcompression of the segments of said chord member between said spacedpanel points, a top truss chord member, and uprights tted between thetop chord member and said laminated and arched bottom chord member.

FREDERIC R. HARRIS.

